Many types of products are created or improved by electron beam (e-beam) processing. Products include appliance parts, gaskets, manifolds, tubing, electrical connectors, molded parts, resin pellets, etc. The possibilities are endless because, in many polymers, property improvements can be attained through e-beam processing. Commodity resins and polymeric materials including polyethylene, ethylene vinyl acetate, polyvinyl chloride, polyamides, and certain types of rubber, such as neoprene, silicone, and ethylene-propylene rubbers, can all realize substantial property enhancement. Property improvements of these polymeric materials may include an increase in tensile strength, impact strength, abrasion resistance, chemical resistance, heat deflection, modulus, hardness, service temperature, barrier properties, crack-resistance, creep resistance, and fatigue resistance. Other special attributes can be imparted to polymers, such as heat-shrink properties, positive temperature coefficient properties, and various other special properties achieved by crosslinking or scission of polymers. Electron beam processing is also used for crystal structure modification (gemstone coloration) and to increase silicon solid-state devices' switching speed, further demonstrating the breadth of possibilities.
Notwithstanding the value of the properties that are created or improved by e-beam processing, efficient radiation techniques are needed. For example, the tray radiation technique for e-beam radiation of bulk material solids is well known. In U.S. Pat. No. 3,766,031 (Dillon), bulk material solids are irradiated in trays. Inefficiencies in this process are due to overscan of the trays with the e-beam and the penetration characteristics (depth-dose) of the electron beam. The latter efficiency loss in the tray irradiation technique arises out of the fact that the dose received by the layer of material varies with its depth. Beam energy and/or material depth are often adjusted so that an equal dose is effected at the opposed surfaces of the material. Radiation in excess of the necessary dose, and radiation that passes entirely through the material, is not utilized. This inefficiency, i.e., the depth-dose characteristic, can cause processing inefficiency of more than 50%, and in some instances may result in undesirable properties in the resulting product.
Improvements in the tray irradiation technique have been achieved as disclosed in U.S. Pat. No. 4,748,005 (Neuberg and Luniewski). In order to overcome the inefficiency of the tray irradiation technique and the most inefficient depth-dose characteristic of processing, a method and apparatus was disclosed in the '005 patent for radiation degradation processing, which makes use of simultaneous irradiation, agitation, and cooling. Agitation of bulk material polymer powder during processing results in a more uniform and efficient method of exposing the polymeric material to radiation. Thus, the prior techniques of irradiation by sequential exposure to doses of radiation were improved according to this technique. Another example of more efficiently irradiating and modifying solid organic polymers with high-energy radiation is disclosed in U.S. Pat. No. 5,916,929 (Knobel and Minbiole). According to this patent, the efficiency of irradiating bulk material polymer solids is improved by passing the solids through an irradiation zone, and irradiating only a central portion of the polymer particles, followed by mixing the irradiated and un-irradiated polymer particles and reintroducing the mixture into the radiation zone for the production of polymer particles which have been more uniformly treated with radiation.
In addition to the above techniques for improvement of electron-beam processing, a number of patents have been granted for processing polymeric bulk material solids, such as polypropylene, and other polyolefin polymers, to improve melt strength, heat resistance, or other physical properties, including U.S. Pat. Nos. 4,916,198; 5,047,446; 5,047,485; 5,541,236; 5,554,668; 5,591,785; 5,605,936; and 5,731,362. In general, the processes described in these patents involve treatment of finely divided polymeric material, which is layered on a traveling belt in the required environment. The speed of the traveling belt is selected so that the layer of finely divided polymeric material passes through the electron beams at a rate to receive the desired dose of radiation. Other process steps may be involved such as treatment of the irradiated polymers in a fluidized bed with nitrogen or inert gas. Expensive equipment is employed to process the polymeric particles in the environmentally-controlled zone.
In summary, there is a need for handling bulk material solids for electron beam processing, and maintaining environmental control during processing. There is also a further need to efficiently control dosage of electron beams and improve on the inefficiencies of the prior art processes. The elimination of expensive processing steps and apparatus of known methods would be desirable. Accomplishing the desired methods, controlling the environment surrounding the product, and achieving other efficiencies and controls would be highly desirable.